Ultrasensitive SERS detection of explosive molecules via iodide-enhanced concentrated silver nanoparticles

Trace detection of nitroaromatic explosives such as 2,6-dinitrotoluene (2,6-DNT) and trinitrotoluene (TNT) is of great significance in the fields of homeland security, anti-terrorism monitoring and environmental governance. Surface-enhanced Raman spectroscopy (SERS) has become a research hotspot in the field of chemical sensing owing to its unique 'fingerprint identification' capacity and high detection sensitivity. Nitroaromatic molecule analytes exhibit weak binding affinity toward conventional citrate-stabilized Ag NPs, which limits the effective adsorption of target molecules to the Ag NPs surface. These conventional substrates only enable detection of 2,6-DNT and TNT at concentrations as high as 10^-1 M and 10^-2 M, respectively. In this study, a surface regulation strategy is proposed by pretreatment highly concentrated Ag NPs with KI to fabricate a high-performance SERS sensing platform on a low-cost aluminum foil substrate. Benefiting from iodide-mediated surface modulation, the detection performance is greatly improved, with distinct characteristic Raman peaks of 2,6-DNT observable at an ultralow concentration of 10^-10 M. I^- can be used as a cleaning agent to effectively remove citrate from Ag NPs surface and provide abundant active sites for the analytes adsorption. In addition, the AgI shell formed on Ag NPs surface by reaction of I^- and Ag⁺ can provide additional chemical enhancement through charge transfer mechanism. This strategy enables highly sensitive detection of nitroaromatic explosives and provides a very competitive solution for the monitoring of trace explosives in the field of public safety.